In recent years, in an image forming apparatus (e.g., MFP), a sheet finishing apparatus is provided adjacent to a post-stage of the MFP to apply finishing to sheets subjected to image formation. The sheet finishing apparatus is called finisher. The sheet finishing apparatus staples or punches sheets sent from the MFP and discharges the sheets from a discharge port to a storage tray.
As an example of a staple unit in the sheet finishing apparatus in the past, there is a sheet processing apparatus disclosed in JP-A-2007-137668.
In the example of JP-A-2007-137668, when a sheet printed by an image forming apparatus is conveyed to a finisher, the finisher conveys, with a conveying roller and a lateral alignment roller (an offset roller), the sheet in the direction of a storage tray. After the sheet passes the conveying roller, the finisher presses the sheet with the lateral alignment roller, moves the sheet in a direction orthogonal to the conveying direction, and presses a side end of the sheet against a positioning wall to laterally align the sheet. The finisher staples a corner portion of laterally-aligned sheets with a stapler.
However, when the lateral alignment of the sheet is performed by using the lateral alignment roller, the lateral alignment roller can move in the direction orthogonal to the conveying direction of the sheet but cannot move in the conveying direction of the sheet. Therefore, even if sizes of sheets are different, the sheets are always pressed in the same position to be laterally aligned. If a size of a sheet is large or small, there is a deficiency in that a lateral alignment failure occurs. When the lateral alignment cannot be satisfactorily performed, sheets cannot be accurately stapled.